Add new tests to the threadtest4.c program. Fix a long-standing data race

in WAL mode for shared-cache.

FossilOrigin-Name: d8d3e6d04cbb9e3033ad8613e3dbd4ad0b01765a

manifest

@@ -1,5 +1,5 @@
-C Remove\sthe\sKeyInfo\scache\s(for\snow\s-\sperhaps\swe\swill\sadd\sit\sback\sin\slater\s-\sor\nmaybe\snot\ssince\sit\sprovides\snegligible\sbenefit\sbut\sadds\sa\slot\sof\scomplexity\nand\sthread-safety\srisk).\s\sAdd\sa\smutex\sto\sATTACH\sto\sdeal\swith\sa\sdata\srace.
-D 2014-12-12T00:52:10.892
+C Add\snew\stests\sto\sthe\sthreadtest4.c\sprogram.\s\sFix\sa\slong-standing\sdata\srace\nin\sWAL\smode\sfor\sshared-cache.
+D 2014-12-12T01:27:17.213
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 6c4f961fa91d0b4fa121946a19f9e5eac2f2f809
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -294,7 +294,7 @@ F src/vacuum.c 9b30ec729337dd012ed88d4c292922c8ef9cf00c
 F src/vdbe.c 1a9e671c9cfc259e4d2affc71f7df4a4c00a842c
 F src/vdbe.h 6fc69d9c5e146302c56e163cb4b31d1ee64a18c3
 F src/vdbeInt.h 9bb69ff2447c34b6ccc58b34ec35b615f86ead78
-F src/vdbeapi.c f8dd2d33a30938188fc292d524e88a91f2e65887
+F src/vdbeapi.c 4bc511a46b9839392ae0e90844a71dc96d9dbd71
 F src/vdbeaux.c 6f7f39c3fcf0f5923758df8561bb5d843908a553
 F src/vdbeblob.c 4af4bfb71f6df7778397b4a0ebc1879793276778
 F src/vdbemem.c 31d8eabb0cd78bfeab4e5124c7363c3e9e54db9f
@@ -913,7 +913,7 @@ F test/thread_common.tcl 334639cadcb9f912bf82aa73f49efd5282e6cadd
 F test/threadtest1.c 6029d9c5567db28e6dc908a0c63099c3ba6c383b
 F test/threadtest2.c ace893054fa134af3fc8d6e7cfecddb8e3acefb9
 F test/threadtest3.c 2b6e07e915c383c250a5b531cf6ef163a3047d7e
-F test/threadtest4.c 38cb574939d5e0c8bd3baa5eb45def2ac6da4db4
+F test/threadtest4.c 1678c340387c19ae28b18e4d8f71d4a989297e46
 F test/tkt-02a8e81d44.test 6c80d9c7514e2a42d4918bf87bf6bc54f379110c
 F test/tkt-26ff0c2d1e.test 888324e751512972c6e0d1a09df740d8f5aaf660
 F test/tkt-2a5629202f.test 0521bd25658428baa26665aa53ffed9367d33af2
@@ -1229,8 +1229,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P fc157dd7f18c94b7ae5f155e1b4a5d7714b7da8c 6bef7ede2bbf0a51729e1943b0b0c895cb57c718
-R 43ea10bc03cfab6b8cae2a465b94aee2
-T +closed 6bef7ede2bbf0a51729e1943b0b0c895cb57c718
+P 03c443eaf24413d6faaa91a33575d9dfd3528b5c
+R 7d057661252570fbf3877a000bcb607e
 U drh
-Z 6886c071ca5a249d6b983c22ce222f5d
+Z 24d2ddd2be9b77d0c401fa6e4cbdad23

manifest.uuid

@@ -1 +1 @@
-03c443eaf24413d6faaa91a33575d9dfd3528b5c
+d8d3e6d04cbb9e3033ad8613e3dbd4ad0b01765a

src/vdbeapi.c

@@ -400,7 +400,10 @@ static int doWalCallbacks(sqlite3 *db){
   for(i=0; i<db->nDb; i++){
     Btree *pBt = db->aDb[i].pBt;
     if( pBt ){
-      int nEntry = sqlite3PagerWalCallback(sqlite3BtreePager(pBt));
+      int nEntry;
+      sqlite3BtreeEnter(pBt);
+      nEntry = sqlite3PagerWalCallback(sqlite3BtreePager(pBt));
+      sqlite3BtreeLeave(pBt);
       if( db->xWalCallback && nEntry>0 && rc==SQLITE_OK ){
         rc = db->xWalCallback(db->pWalArg, db, db->aDb[i].zName, nEntry);
       }

test/threadtest4.c

@@ -16,13 +16,17 @@
 ** This test program runs on unix-like systems only.  It uses pthreads.
 ** To compile:
 **
-**     gcc -o tt4 -I. threadtest4.c sqlite3.c -ldl -lpthread
+**     gcc -g -Wall -I. threadtest4.c sqlite3.c -ldl -lpthread
 **
 ** To run:
 **
-**     ./tt4 10
+**     ./a.out 10
 **
-** The argument is the number of threads.
+** The argument is the number of threads.  There are also options, such
+** as -wal and -multithread and -serialized.
+**
+** Consider also compiling with clang instead of gcc and adding the
+** -fsanitize=thread option.
 */
 #include "sqlite3.h"
 #include <pthread.h>
@@ -40,6 +44,7 @@
 typedef struct WorkerInfo WorkerInfo;
 struct WorkerInfo {
   int tid;                    /* Thread ID */
+  int nWorker;                /* Total number of workers */
   unsigned wkrFlags;          /* Flags */
   sqlite3 *mainDb;            /* Database connection of the main thread */
   sqlite3 *db;                /* Database connection of this thread */
@@ -284,7 +289,7 @@ static void *worker_thread(void *pArg){
   sqlite3_stmt *pStmt;
 
   printf("worker %d startup\n", p->tid);  fflush(stdout);
-  for(iOuter=1; iOuter<=4; iOuter++){
+  for(iOuter=1; iOuter<=p->nWorker; iOuter++){
     worker_open_connection(p, iOuter);
     for(i=0; i<4; i++){
       worker_add_content(p, i*100+1, (i+1)*100, (p->tid+iOuter)%3 + 1);
@@ -303,6 +308,17 @@ static void *worker_thread(void *pArg){
     if( p->nErr ) break;
     sqlite3_finalize(pStmt);
 
+    if( ((iOuter+p->tid)%3)==0 ){
+      sqlite3_db_release_memory(p->db);
+      p->nTest++;
+    }
+
+    if( iOuter==p->tid ){
+      pthread_mutex_lock(p->pWrMutex);
+      run_sql(p, "VACUUM");
+      pthread_mutex_unlock(p->pWrMutex);
+    }
+
     worker_delete_all_content(p, (p->tid+iOuter)%2);
     worker_close_connection(p);
     p->db = 0;
@@ -362,6 +378,8 @@ int main(int argc, char **argv){
        "Options:\n"
        "  --serialized\n"
        "  --multithread\n"
+       "  --wal\n"
+       "  --trace\n"
        ,argv[0]
     );
     exit(1);
@@ -406,6 +424,7 @@ int main(int argc, char **argv){
   memset(aInfo, 0, sizeof(*aInfo)*nWorker);
   for(i=0; i<nWorker; i++){
     aInfo[i].tid = i+1;
+    aInfo[i].nWorker = nWorker;
     aInfo[i].wkrFlags = wkrFlags;
     aInfo[i].mainDb = db;
     aInfo[i].pWrMutex = &wrMutex;